JPS61293465A - Sterilizing system by hydrogen peroxide plasma - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the sterilization of articles in gaseous plasmas, and more particularly to the use of hydrogen peroxide in plasmas to annihilate microorganisms on articles such as food surfaces and medical instruments. Regarding things.

Various sterilization methods have been utilized in the past to sterilize different types of articles, including disposable and reusable medical devices, food products, and food containers. Steam or dry heat sterilization, which was widely used in the past, is not useful for sterilizing materials that are adversely affected by this type of heat or steam. Ethylene oxide gas has also been used, but can leave toxic residues on the items to be sterilized, which can lead to
In particular, they suffer from the disadvantage of potentially adverse effects on patients who come into contact with articles of this type.

The long aeration cycles required to remove residual ethylene oxide from sterilized articles also make ethylene oxide sterilization very tedious.

The use of plasma to sterilize containers was suggested in US Pat. No. 3,383,163.

A plasma is an ionized form of a gas that can be generated by the application of electrical power from different sources. The ionized gas will come into contact with and effectively destroy microorganisms on the surface of the article to be sterilized.

US Pat. No. 3,851,436 discloses the use of a radio frequency generator to generate such a plasma from an inert gas such as argon, helium or xenon. US Pat. No. 3,948,601 also discloses the use of a radiofrequency generated plasma that ionizes argon, nitrogen, oxygen, helium or xenon.

The method described in the above-mentioned patent requires direct contact of the surface of the product to be sterilized with the plasma, which product must not be packaged at the time of sterilization. Practical sterilization methods utilized to sterilize single-use medical items generally require packaging of the medical item prior to sterilization. This is because if the product is packaged following sterilization, there is a possibility of microbial contamination.

US Pat. No. 4,207,286 discloses a gaseous plasma sterilization system using glutaraldehyde as the gas utilized in the plasma sterilization system. The article to be sterilized is placed in an open container or package and then subjected to a sterilization cycle. When the sterilization cycle is finished, the container is sealed.

This container is opened during the sterilization cycle to allow gas to flow into its interior, bringing this gas into contact with any microorganisms that may be present on the surfaces of the articles to be sterilized.

US Pat. No. 4,321,232 discloses a plasma sterilization system in which the articles to be sterilized are placed in a package made of porous material. The gas used in this method is oxygen, and it has been shown that sterilization can be accomplished through porous packaging within 60 minutes.

US Pat. No. 4,348,357 discloses a plasma sterilization method using oxygen, nitrogen, helium, argon or Freon as the gas. The pressure is pulsating;
That is, the pressure within the container is cyclically increasing or decreasing alternately. Additionally, the plasma can be de-energized during the pressure reduction portion of the pressure cycle to reduce the heating effect on the articles to be sterilized.

JP-A-58-103460 is a plasma sterilization method,
The gas consists of nitrous oxide or a mixture of nitrous oxide and other gases, such as oxygen, helium or argon. Furthermore, it is stated that this method can be used for sterilization via packaging, particularly via packaging prepared from polyethylene trifluoride or polyethylene tetrafluoride resins or paper coated with these materials.

Special IJ No. 58-162276 discloses the sterilization of foods using nitrogen oxide gas or a mixture of nitrogen oxide gas and ozone in a plasma.

All of these conventional plasma sterilization systems have never been put into widespread use due to limitations such as the time required to perform sterilization, the temperatures available in the sterilization technique, or the need for post-sterilization packaging. This is due to special requirements regarding the process.

Hydrogen peroxide is known to have disinfectant properties and has also been used in solutions to kill bacteria on various surfaces. U.S. Patent No. 4,437,56
No. 7 discloses the use of aqueous hydrogen peroxide solutions at low concentrations, ie 0.01 to 0.10% by weight, to sterilize medical or surgical packaging products. Sterilization at room temperature requires at least 15 days. At higher temperatures, sterilization can be accomplished in about one dayb U.S. Pat.
No. 4 and No. 4.230,663 disclose the use of hydrogen peroxide in one gas phase at a temperature of 80° C. and a concentration of 0.10 to 75 μH2O2 vapor/L for sterilization and disinfection. There is. Depending on concentration and temperature, sterilization times have been reported to vary from 30 minutes to 4 hours.

U.S. Pat. Nos. 4,366,125 and 4.2, U.S. Pat.
No. 89,728. The lack of penetration by UV radiation below the surface of the article to be sterilized limits the action of this effect on clear solutions or surfaces that can be exposed directly to radiation. Articles in opaque packaging or in transparent packaging that absorb ultraviolet light cannot be sterilized.

Food packaging materials sterilized with hydrogen peroxide should be sterilized prior to use.
Hydrogen peroxide must be removed from the material.

Contains residue. U.S. Patent No. 4,368. ()
No. 81 discloses the use of antioxidants or reducing agents, such as L-ascorbic acid, to remove residual hydrogen peroxide from sterile food packages.

The combination of hydrogen peroxide and plasma has never been used for sterilization before.

The present invention incorporates the use of hydrogen peroxide as a precursor of active species in a low temperature plasma sterilization system. This sterilization method provides initial contact of the material to be sterilized with hydrogen peroxide prior to generation of plasma at a power level sufficient to effect sterilization. It has been found that employing an initial contact period with hydrogen peroxide can significantly reduce the total time and power required to achieve sterilization by cold plasma. Additionally, pretreatment with hydrogen peroxide is also employed.

It allows sterilization to occur in many different types of packaging materials.

Since the H2O20 decomposition products in the plasma contain water, oxygen and hydrogen, no toxic residue remains on the sterilized article after plasma treatment.

The method of the present invention differs from prior art gas plasma sterilization methods in two important features. The first is the use of hydrogen peroxide vapor as a precursor of reactive species, rather than inert gases such as oxygen, nitrogen, etc. The second major difference is the adoption of a pretreatment period in which hydrogen peroxide vapor is brought into contact with the article to be sterilized prior to the application of power at the level required to effect sterilization. The article is placed within a plasma chamber, the chamber is closed, and a vacuum is applied to the chamber to remove any gas present within the chamber. An aqueous solution of hydrogen peroxide is then injected into the chamber, raising its pressure to a level of about 0.1 to 10)-L. The hydrogen peroxide remains in the chamber for a sufficient period of time, typically 5 to 30 minutes, to bring it into intimate contact with the article to be sterilized before the plasma is generated at a power level sufficient to achieve sterilization. do. Next, hold the power for no more than 50 minutes to achieve complete sterilization◇
However, sterilization can be effected in as little as 5 minutes after initial plasma generation, depending on the concentration of hydrogen peroxide in the chamber and the power applied within the chamber. It is also possible to perform the pretreatment step outside the plasma chamber. It is also possible to place the articles to be sterilized in a vacuum chamber where plasma cannot be generated.The chamber is evacuated and hydrogen peroxide is injected into the vacuum chamber. The articles to be sterilized are held in a vacuum chamber for the desired pretreatment time and then exposed to plasma.
is placed in a chamber and a plasma will be generated.

The materials or articles to be sterilized by this method may be packaged in a variety of commonly available packaging materials used for sterile products. A preferred material is a spunbonded polyethylene packaging material commonly available under the trademark TYVBK'J, or a composite consisting of ``TYVBK'' and a polyethylene terephthalate packaging material commonly available under the trademark ``Mylar.'' It is the material. Other similar packaging materials can also be used. Additionally, paper packaging materials can also be used. Regarding paper packaging materials,
Longer processing times may be required to achieve sterilization. This is because of the possible interaction of hydrogen peroxide and other reactive species with the 9 paper.

Plasma is generally generated by an electrical discharge in a gas. Plasma generated at atmospheric pressure or higher pressure is an "arc"
or high-temperature plasma, and plasma generated at 0 reduced pressure, i.e. 10-5 to 102 Torr, which may involve temperatures exceeding 1000 degrees Celsius, is called "glow discharge" or low-temperature plasma, and may involve temperatures exceeding 1000 degrees Celsius. Accompanied by temperatures ranging from several hundred degrees. The low temperature plasma of the present invention is preferably generated at a pressure of less than 10 Torr, and generally 1
with temperatures below 00°C.

As used in this application, the term "plasma"
Electrons, ions, free radicals, dissociated and/or excited atoms produced by an applied electric field are any part of a gas or vapor containing molecules and any concomitant ionization that may be produced. Intended to include those involving radiation. The applied electric field covers a wide frequency range, but high frequencies are commonly used.

Plasma sterilization usually involves trapping chamber 2 as shown in the figure.
It is done within 0. This chamber includes a door or opening 10 through which the articles to be sterilized can be introduced. The chamber also includes an inlet 11 for injecting gas into the chamber and a line 12 connected to a vacuum bonder, thereby allowing the chamber to be evacuated. The gas inlet line 11 is provided with a pipe connection 14 for introducing an aqueous solution of hydrogen peroxide into the chamber 20 . The chamber includes a radio frequency electrode 13, which can be wrapped around the entire chamber or placed on the sides of the chamber and the radio frequency generator to generate the necessary radio frequency signal. Coupling of the RF power from the output of the matching network to the discharge is done by sections of coils or capacitor plates.

These 281 types of coupling are called inductive coupling and capacitive coupling, respectively. Various control devices for controlling the generation of high frequency signals are also used and shown in the figures, including function generators, RF power amplifiers, power meters and matching networks. A matching network matches the amplified RF flaw signal input to the coil. A plasma is generated by evacuating a chamber, introducing a gas or vaporized liquid, and turning on power to the electrodes.

This plasma is generated in the present method in the same manner as in the prior art plasma sterilization systems described above.

The plasma used in the method may be continuous or pulsatile.

That is, the power may be applied continuously, or the power may be activated in a periodic manner while maintaining the plasma pressure constant. The use of a pulsating plasma prevents overheating of the gas within the chamber, as well as overheating of the articles that may be desired to be sterilized. The pulsation sequence can be varied over a fairly wide range (without risking overheating of any article).

Generally, the pulsation sequence is a ratio of power on to power off. For example, with a 1:2 pulsating plasma, power would be applied for 5 milliseconds, then turned off, and then applied again for 1.0 milliseconds at the edge. No particular pulsation sequence is definitive. This power is applied over a period of time measured in minutes rather than seconds. The purpose of pulsation is to avoid overheating of the article to be sterilized, so any pulsation sequence that avoids overheating and achieves sterilization within a reasonable time may be used. .

Continuous plasma can also be used, provided there is little risk of overheating the articles to be sterilized.

As previously indicated, in the present method hydrogen peroxide is injected into the plasma chamber prior to application of the power necessary for sterilization. The hydrogen peroxide is injected in the form of an aqueous hydrogen peroxide solution containing about 3 to 20% by weight hydrogen peroxide. The concentration of hydrogen peroxide vapor in the chamber may be within the range of 0.05 to 10 μm of hydrogen peroxide per liter of volume. Higher concentrations of hydrogen peroxide will result in shorter sterilization times. A concentration of 0.125 mg per liter is the lowest preferred concentration of hydrogen peroxide. Air or an inert gas such as argon, helium, nitrogen, neon or xenon may be added along with the hydrogen peroxide to maintain the pressure within the chamber at the desired level. The hydrogen peroxide solution may be injected in two or more parts. For example, at time "zero" the total amount of hydrogen peroxide solution to be used, V2, is injected into the chamber, and 5
After a few minutes, the remainder of the hydrogen peroxide solution can be sprayed out.

Thereafter, the hydrogen peroxide will remain in the chamber until power is applied for an additional 5 to 10 minutes. Clearly, the pretreatment time is intended to allow the hydrogen peroxide to diffuse through the packaging material and into close proximity, if not contact, with the surfaces of the articles to be sterilized. As a result of the application of power to the radio frequency generator, sporicidal active species are produced by a combination of hydrogen peroxide and plasma, whereby the time required to effect sterilization is shorter than in prior art methods. Although it is possible to generate plasma at low power levels during the pretreatment cycle,
There is no particular advantage to applying power during the pretreatment cycle.

The exact mechanism of sporicidal activity is not known with universal validity, but upon discharge hydrogen peroxide releases free radicals,
That is, there is a possibility of dissociating into OH+02H,H [M, Ven.
``Plasma Chemistry and Plasma Processing'' by Ugopalan and A, 5hih)
is-try and plasma process
ing) J Vol. 1, No. 2, pp. 191-199, 19
1981]. These free radicals, alone or in combination with hydrogen peroxide, are likely the primary source of sporicidal activity. Ultraviolet light also generates a cold plasma and can play a role in sporicidal activity in the presence of % hydrogen peroxide.

The general operation of the invention is as follows.

1) Place the object or article to be sterilized in a vacuum chamber or plasma chamber.

2) Evacuate the chamber to a pressure of approximately 0.05 - liters.

3) Inject an aqueous solution of hydrogen peroxide into the chamber as a pressure sail of 5 to 10 torr of vaporized water and hydrogen peroxide. The preferred pressure is 1 to 2 torr. The concentration of hydrogen peroxide injected into the chamber is approximately 0.5 to 1.
It is sufficient if it is 0 ■/chamber volume liter. The preferred concentration is 0.208 mg/liter.

4) The object to be sterilized is placed in the chamber for approximately 5 to 3 hours before a plasma with sufficient power to sterilize is generated.
Retained for a period of 0 minutes. This period is referred to herein as pre-processing time. Pretreatment times of 30 minutes or more are also available. The duration of pretreatment depends on the type of packaging used, the number of articles to be sterilized, and the placement of the articles within the chamber.

5) The objects to be sterilized are exposed to plasma in a pretreatment chamber or a separate plasma chamber.

6. The RF energy utilized to generate the plasma may be continuous or it may be pulsatile. The object remains in the plasma for 5 to 60 minutes to achieve complete sterilization.

During plasma treatment, hydrogen peroxide is decomposed into non-toxic products and therefore no additional hydrogen peroxide is required to remove residual hydrogen peroxide from the object to be sterilized or its packaging prior to use of said object. No process is required.

In the examples below, the efficacy of the sterilization cycle is tested (
It is expressed as the ratio of the number of bacteria that survived the test (S) to the initial number of bacteria placed on the specimen prior to So). In all of these examples, the bacteria tested were Bacillus subtilis (Gl
var. obigii)] spores, which were placed on a vapor disk and packaged in a spun-bonded polyethylene package.

All examples were operated at a frequency of 2.49 MHz with the exception of Example V, which was conducted at a frequency of 3-89 MHz.
The experiments were carried out in a plasma chamber of 5 L/l/l.

Example I Table 1 contains a comparison of the sporicidal activity of the hydrogen peroxide/plasma system of the present invention versus other conventional gases in the plasma cycle of the present invention. All tests were conducted under the same reaction conditions: 0.5 ms plasma on for 15 min.

and 1.0 ms plasma, 150 at off.
It was carried out under Watsuto's pulsating plasma. All tests used a 10 minute pretreatment cycle with the gases listed in the table. All pre-treatments and plasma treatments were performed at a pressure of 1.5 Torr. The glutaraldehyde and hydrogen peroxide pretreatment cycles contained 0.208 mg/IJ liter of glutaraldehyde and hydrogen peroxide each. The results are expressed as S/So, where S is the number of surviving bacteria and SO is the initial number of bacteria.

Table ■ Sporicidal activity of H2O2/plasma system compared to other gas/plasma systems Q29. lX10 /1
．． 3X10 -0.72N20 4.9X
1011/1.6X105-0.31 5.7X10'/1.1X10' -0,5
Only the 2H2020/3.4X105-0 hydrogen peroxide/plasma system showed good sporicidal activity and sterilized the treated articles.

Example ■ The effect of hydrogen peroxide concentration in the plasma chamber on sporicidal activity was determined by pretreatment test samples with different concentrations of hydrogen peroxide vapor for 10 minutes at 1.0 μl pressure. . The treated samples were then exposed to a 200 watt pulsating plasma for 15 minutes with a period of 0.5 msec plasma on and 1.0 msec plasma off. 2 woodcutter contrasts, i.e. 1
One type uses only hydrogen peroxide, and the other type uses water plasma.
One utilizing only a) was also implemented. The results are shown in Table 3.

Chapter ``Effect of H2O2 concentration on surface sporicidal activity 0''
1.0 1.0.125
1.0 7,3X10-2.208
1.0 1.4X10”-2・416
1.0 0★★, 625
9. 1X1O-20゜★ In this test, plasma containing 4.16■H2Q/+) liters was used.

★★ 2.4 x 10 bacteria wiped out.

At concentrations below 0.625 mg/liter, water plasma treatment alone or H20□ alone did not produce any significant sporicidal activity.

However, a significant enhancement in sporicidal activity was obtained with the H2O2/plasma combination at the total H2O2!1 degrees evaluated.

(Example I) The effect of pressure on sporicidal activity was investigated at hydrogen peroxide concentrations of 0.
208 mg/liter and using the same pretreatment and plasma cycle as in Example H. Activity was measured at pressures of 0.5, 1.0, 1.5 and 2.0 Torr. Air plasma only and hydrogen peroxide only were also measured. The results of these experiments are reported in Table 1.

Table ① Effect of pressure on sporicidal activity of H2O2 plasma = 1 1.0 6.7X10 1.0 1.
4X10'★3.4X10 bacteria wiped out.

Low level activity at all pressures was obtained with plasma alone or H20□ alone. Optimal activity with the H2O2 plus plasma system was obtained at a pressure of 1.5 Torr (Example ■) The effect of plasma power on sporicidal activity was determined at a pressure of 1.5 Torr.
It was determined using hydrogen peroxide at a concentration of 0.208 H20/liter at a pressure of Torr. No (war level is 5
They were 0,100,150 and 200 watts. The plasma was pulsed as in Example ■, and the sample was pretreated for 10 minutes by the method used in Example ■. Air plasma only and hydrogen peroxide only tests were also conducted and the results are shown in Table ■ Table ■ Effect of RF power level on sporicidal activity of air plasma and H20□ plus plasma 0 1.
0 4. oxio-”50 4
．． 0X10-18. lX1O-11006,7X10-
12.5X10''150 2.4X10-1
0”200 3.9X10-”
0”★1.8X10 bacteria wiped out.

Low levels of sporicidal activity were obtained with air plasma alone at all power loads evaluated. Significant sporicidal activity was obtained with the H2O2 plus plasma system at 100W and sterilization was achieved at 150 and 200W (Example V). The effect of plasma generation was determined using a hydrogen peroxide concentration of 0.208 μH2O2/Litya at a pressure of 1.5 Torr (1.5 Torr) during a 10-minute hydrogen peroxide pretreatment time.
0,125 and 150) (3.89 M)l
applied at z. The plasma was pulsated with a power of 0.5 milliseconds and a cycle of on, whir, and off of 1.0 milliseconds. After 10 minutes of pretreatment, all samples were
Exposure to a 150 watt blower pulsating from milliseconds on to 1.0 milliseconds off for 15 minutes. The results of this test are shown in Table V.

Table 7 Effect of U power level during pretreatment on sporicidal activity of H20□ plus plasma 50 9.4X10-'75
1.2X10-'100
1.0 125 0.133150
Significant sporicidal activity was obtained when low power levels, 50 and 75 watts, were applied during the 0.94 hydrogen peroxide pretreatment time. Before hydrogen peroxide can diffuse into the sample,
At higher power levels, where more of it would be diffused, very limited sporicidal activity was seen.

(Example ■) The pulsating effect of plasma power on sporicidal activity was determined using a hydrogen peroxide concentration of 0.208 ■H2O2/'') Torr and a pressure of 1.5 Torr.The samples were as in Example ■, Pre-treated with hydrogen peroxide for 10 minutes. Air plasma only and hydrogen peroxide only tests were also performed. As in the previous test, the hydrogen peroxide only test was approximately 4.0 x 10-1 Testing with 100 watts of continuous plasma for 5 minutes and pulsing for 15 minutes with cycles of 0.5 ms plasma, on, and 1.0 ms plasma, off resulted in an S/SO value of The results of the test using 150 watts of plasma are shown below.
Shown in the table.

Chapter ■ Table Effect of plasma pulsation on sporicidal activity★2.2X10
5 bacteria wiped out.

The results of these tests indicate that sterilization can be achieved by continuous plasma treatment within 5 minutes.

(Example ■) The effect of repeated H2O2/plasma treatments on sporicidal activity was evaluated using hydrogen peroxide concentrations of 0.125 mg/liter and 1
．． Determined using a pressure of 5 torr. Each treatment cycle is H2O
2 10 min pretreatment time and pulsating plasma 20
It consisted of a 15 minute exposure to 0 watts (0.5 ms plasma on and 1.0 ms plasma off). The effects of 1 and 2 treatment cycles are shown in Table 3.

Table Ⅲ Effect of number of H2O2/plasma cycles on sporicidal activity 1 5.9X10-16.6X10"-18,8X
10-'2 8.2X10'''' 1.8X1
0-10" 2°5 x 10 bacteria wiped out.

These results indicate that sterilization can be achieved at low H2O2 concentrations by exposing the sample to two H2O2/plasma treatment cycles.

The above examples demonstrate the effectiveness of using hydrogen peroxide as a precursor of reactive species in plasma sterilization methods. The operating parameters of this method, namely hydrogen peroxide concentration, pretreatment period, applied power and duration of plasma generation, can be varied within fairly wide limits to produce a suitable sterilization cycle. If the duration of plasma generation increases, the applied power or hydrogen peroxide concentration can be decreased, and similarly, if the hydrogen peroxide concentration or applied power increases, the duration of plasma generation can be decreased. I can do it.

(Example ■) Since the temperature of the article to be exposed to plasma increases, experiments were conducted to compare the sporicidal activity obtained with hydrogen peroxide and heat to that obtained with hydrogen peroxide and plasma. Ta. This test was performed by placing samples inside and outside a wire cage within a plasma chamber. Since metal effectively shields RF radiation, the sample inside the wire cage was to be shielded from RF radiation and plasma generation, but not from exposure to hydrogen peroxide vapor or heat generated by the plasma. It's not a translation. The samples were treated with 0.208 μm hydrogen peroxide/liter for 10 minutes at a pressure of 1.5 Torr. The treated samples were then exposed to a pulsed plasma (150 W) for 15 minutes with a period of 5 msec plasma on and 1.0 msec plasma off.

The temperature of the nylon blocks placed inside and outside the wire cage was measured using the Luxtrori model (Luxtrori model).
Model) 100OA, rfluorobutic (FL)
Monitored with UOROPTIC) J thermometer. At the end of the plasma treatment, the temperatures recorded inside and outside the wire cage were 52.1°C and 56.9°C, respectively. The results of the sporicidal activity test are shown in Table ■■.

A control experiment using only hydrogen peroxide vapor was also carried out to compare sporicidal activity with plasma H2O2 + plasma ff 2.4X10-"
O”★★3.0X 105 spores were completely destroyed.

These results indicate that significantly better sporicidal activity was obtained with the combination of hydrogen peroxide and plasma inside the wire cage than outside. The decrease in sporicidal activity inside the wire cage can be attributed in large part to the lack of plasma production. This is because similar sporicidal activity was obtained with hydrogen peroxide alone inside and outside the cage, and the temperatures inside and outside the wire cage were similar after plasma treatment.

[Brief explanation of drawings]

The figure is a schematic diagram showing a plasma reactor used in the present invention. 10...door or opening, 11...entrance, 12...
Pipe line, 13... High frequency electrode, 14... Pipe connection port, 2
0...Chamber. Patent applicant: Surgicos Incorporated (
2 people outside) −=−・・・′

Claims (9)

[Claims] (1) placing an article to be sterilized in a chamber; contacting the article with hydrogen peroxide vapor for a sufficient time to bring the hydrogen peroxide into intimate contact with the article; and A sterilization method comprising the steps of: generating plasma around the article; and retaining the article in the plasma for a sufficient period of time to effect sterilization. 2. The method of claim 1, wherein the hydrogen peroxide concentration in the chamber is at least 0.05 mg per liter of chamber volume. (3) The method according to claim 1, wherein the plasma is pulsated. (4) Plasma power-on-power-off ratio 1:
4. A method as claimed in claim 3, wherein the pulses are pulsated at .2. (5) The method according to claim 1, wherein the hydrogen peroxide concentration in the chamber is 0.05 to 10 mg/liter based on the chamber capacity. (6) The method according to claim 1, wherein the concentration of hydrogen peroxide is 0.208 mg/liter. (7) The method according to claim 1, wherein the pretreatment time is 5 to 30 minutes. (8) The method according to claim 1, wherein the plasma is generated over a period of 5 to 60 minutes. (9) The method of claim 1, wherein the hydrogen peroxide and plasma treatment cycles are repeated.